1. Field of the Invention
This invention relates generally to a downhole filtration tool for use in oil, gas, and water wells, and more particularly to a downhole filtration tool having a carbon steel mandrel surrounded by a non-metallic element giving the filter improved permeability, resistance to chemical breakdown, and physical strength.
2. Description of the Related Art
Oil and gas wells and water wells include a wellbore extending into a well to some depth below the surface. Typically, the wellbore is lined with casing to strengthen the walls of the borehole. To further strengthen the walls of the borehole, the annular area formed between the casing and the borehole is typically filled with cement to permanently set the casing in the wellbore. The casing is then perforated to allow production fluids to enter the wellbore and be retrieved at the surface of the well.
Various types of downhole equipment, such as pumps and similar devices, are used to move production fluids from within the wellbore to the surface. A typical downhole arrangement would include a string composed of a series of tubes or tubing suspended from the surface. One type of well-known pump is a downhole electrical submersible pump (ESP). The ESP either includes or is connected to a downhole motor which is sealed so that the whole assembly is submerged in the fluid to be pumped. The motor is connected to a power source at the surface and operates beneath the level of the fluid downhole in order to pump the fluid to the surface. A component is connected to the motor which prevents well fluid from entering the motor and equalizes internal motor pressure with the well annulus pressure.
A number of factors may be detrimental to the production of the ESP, such as the presence of foreign solid particles, such as sand, sediment, and scale. The amount and size of sand and other solid particles in the fluid may vary widely depending on the well and the conditions encountered. In enhanced recovery operations, for example, fluids may be pumped down the well to stimulate production causing additional movement of sands and solids. The sand and other solid particles act as abrasives and, over time, are damaging to the operation of the pump.
Yet another problem typically encountered in wells is an excess amount of gas or gas bubbles entering the intake of the pump causing the pump to decrease in efficiency. ESPs have dramatically lower efficiencies with significant fractions of gas, and at some point, the pump may become “gas locked” and damage to the pump and/or motor may result.
Many types of filters have been designed for use with ESPs. Such filters typically include a filter element designed to screen solid particles from the pump intake; however, the filtered particulates often become entrapped in the filter element. The amount of particulate material collected on the filter element is directly proportional to the to the pressure drop that occurs across the filter element. Since an excessive pressure drop across the filter element can significantly reduce fluid flow, the filter element must be periodically changed or cleaned. Often, this is done by removing the ESP from the fluid and removing the filter element. This can be a timely and inconvenient process. Pumps with intricate backwashing systems have been designed, but these are often expensive and cannot be used to retrofit existing systems. As a result, many pumps are generally operated without any filter and therefore experience early pump failure and extensive and costly down time.
A problem associated with conventional downhole filtration tools arises in high temperature and/or high pressure applications. High downhole temperatures are generally above 200° F. and up to 450° F., while high downhole pressures are generally above 7,500 psi and up to 15,000 psi. Another problem with downhole filtration tools occurs in both high pH (e.g., more than 8.0) and low pH (e.g., less than 6.0) environments. In these extreme downhole conditions, conventional filters become ineffective and suffer from degradation.
It is therefore desirable to provide an improved downhole filtration tool for use in oil, gas, and water wells.
It is further desirable to provide a downhole filtration tool that is connected to and suspended from downhole equipment, such as but not limited to, an ESP and operates as an intake to the pump.
It is still further desirable to provide a downhole fluid filtration tool capable of separating sand and other solid particles from production fluid while also preventing an undue amount of gas from entering the pump.
It is yet further desirable to provide a downhole filtration tool having a carbon steel mandrel surrounded by a non-metallic filter element giving the downhole filtration tool improved permeability, resistance to chemical breakdown, and physical strength.